D-isoascorbic Acid Research Articles

Rapid determination of 54 dye components in hair dyes by liquid chromatography coupled to quadrupole orbitrap high-resolution mass spectrometry.

Chemical hair dye components can have allergenic, reproductive, and carcinogenic risks. Detecting restricted and prohibited ingredients in these products is challenging due to product diversity, isomer separation, instability, and wide polarity range. A method was developed using HPLC-high-resolution mass spectrometry for the qualitative and quantitative analysis of 54 hair dye components in various products. Samples were extracted with a 70% methanol solution, ultrasonicated in an ice bath, centrifuged, filtered, diluted with 25% methanol solution and 25% methanol solution containing 0.05% D-isoascorbic acid. Separation was achieved using an ACE Excel 3 C18 column (2.1 mm × 150 mm, 3 μm) with analysis conducted via quadrupole Orbitrap mass spectrometry. It showed good linear correlations, with detection limits of 0.1-23.5 ng mL-1, and quantitation limits of 0.2-78.1 ng mL-1. Average recovery ranged from 60.0% to 118.4%, with repeatability from 4.0% to 14.9%. Stability was confirmed within 48 hours. When applied to 20 batches of commercially available hair dyes, 24 hair dye components were found within permissible levels. The method is crucial for quality control of hair dyes, covering 10 common prohibited and 44 permissible hair dye components outlined in the Safety and Technical Standards for Cosmetics (2015 Edition). Compared to the standard methods, it can separate isomers in a single mobile phase system within 15 minutes in positive ion mode while maintaining sensitivity for phenol, hydroquinone, and other components in negative ion mode. Moreover, the pre-treatment strategy significantly improved stability and accuracy, enabling precise analysis of the 54 hair dye components.

Identifying dominant spoilage fungal species and preservative treatments for extending shelf life of whole lotus rhizomes at 4 °C

A preservative for whole lotus rhizome preservation was developed under 4 °C storage in this study. The study included the following steps: Firstly, isolation and identification of spoilage causing fungi of lotus rhizome, and four main spoilage causing fungi were identified, including Penicillium solitum, Geotrichum silvicola, Phytopythium helicoides, and Pseudeurotium zonatum. Secondly, selection of antifungal agent with good inhibitory ability against the above four spoilage causing fungi, finally 0.5 % potassium sorbate was selected considering edible security at the same time. Thirdly, the selection of suitable color fixative according to the indexes of root skin and flesh color differences, and sensory evaluation. The final color fixative composition: EDTA-2Na (8 g/L), ascorbic acid (8 g/L), and d-isoascorbic acid sodium (6 g/L). Finally, the antifungal agent and color fixatives were mixed to make the preservative. Soaked in preservative for 20min, drained and packed into PE bags, vacuumed and stored at 4 °C, the lotus rhizomes could maintain better color, got high sensory score, soluble solids content, and total acid content, and the microbial counts were always lower than the untreated group. The preservative could extend the shelf life of whole lotus rhizome to about 50 d at 4 °C.

Photostability of vitamin C in industrialized fruit juices and isomers determination by HPLC-DAD

L-ascorbic acid (LAA) and D-isoascorbic acid (DIAA) are two of the most important antioxidants in industrialized fruit products as mixed fruit juices, fruit concentrates, and jams, in which they are added as antioxidants and as a nutrient. Despite that, LAA may undergo oxidative- and photo-degradation during storage, compromising its concentration and activities in these food products. In this work we aimed to optimize a method for the identification and quantification of LAA and DIAA by high performance liquid chromatography with diode-array detection (HPLC-DAD) using a NH2 column and a pre-heated mobile phase. A further aim was to investigate if food packing actually protects fruit juices against LAA photodegradation. For the UV photostability test, samples were UV-irradiated at 1416 μW cm−2, at 28 ± °C, and with a radiation energy above 200 W h m−2. The optimized HPLC method provided complete peak resolution of vitamin C isomers in less than nine min run-time. At the end of photostability tests with fruit juices and jellies packaged in polyethylene terephthalate and glass bottles or flasks, L-ascorbic acid was undetectable, suggesting that the packages did not provide effective protection against vitamin C photodegradation. To the best of our knowledge, vitamin C photostability in fruit products was previously unreported.

Synthesis and potential antidiabetic and lipid-lowering activities of putative asperidine B and its desmethyl analogue

Putative asperidine B is an unnatural 2,6-disubstituted piperidin-3-ol and a structural isomer of (+)-preussin, a well-known pyrrolidin-3-ol alkaloid. This work reports the first enantioselective synthesis of putative asperidine B and its desmethyl analogue via a chiron approach starting from d-isoascorbic acid as well as evaluation of their free-radical scavenging, antidiabetic, and anti-hyperlipidemic activities. Both putative asperidine B and its desmethyl analogue markedly reduced the total reactive oxygen species (ROS) without cytotoxicity in hepatocellular carcinoma (HepG2) cells. The desmethyl analogue was a potent inducer for two antioxidant gene expression, glutathione peroxidase and superoxide dismutase, whereas putative asperidine B only induced superoxide dismutase. In addition, putative asperidine B exerted potent antidiabetic activity via α-glucosidase inhibition (IC50 = 0.143 ± 0.001 mg/mL) comparable to that of acarbose, an antidiabetic drug. Consistent with the parent asperidine B (preussin), both putative asperidine B and its desmethyl analogue inhibited cholesterol absorption in the intestinal Caco-2 cells. These novel and promising antioxidant, antidiabetic, and lipid-lowering effects of piperidin-3-ols could offer a starting point for this class of compounds for obesity and diabetic drug discovery.

Effects of Different Bacteriostats on the Dynamic Germination of Clostridium perfringens Spores.

Bacteriostats, as chemical substances that inhibit bacterial growth, are widely used in the sterilization process; however, their effects on spindle spores are unclear. In this study, the effects of bacteriostats, including nine commonly used food additives and four detergents, on the growth of Clostridium perfringens spores were investigated. The results showed that 0.07‱ ethylenediaminetetraacetate had a good inhibitory effect on C. perfringens spore growth, and the spore turbidity decreased by 4.8% after incubation for 60 min. Furthermore, 0.3‱ tea polyphenols, 0.8‱ D-isoascorbic acid, and 0.75‱ potassium sorbate promoted leakage of contents during spore germination. Among the four detergents, 5‱ glutaraldehyde solution presented the best inhibitory effect on the growth of C. perfringens spores, and the spore turbidity decreased by 5.6% after incubation for 60 min. Further analysis of the inactivation mechanism of spores by the bacteriostats was performed by comparing the leakage of UV-absorbing substances during germination. The results revealed that bacteriostats could not directly kill the spores, but could inactivate them by inhibiting germination or damaging the spore structure during germination, thus preventing the formation of bacterial vegetative bodies. These findings provide important information and reference for the mechanism underlying the effects of different bacteriostatic agents on spore growth.

Synthesis and Characterization of Bimetallic Nanoclusters Stabilized by Chiral and Achiral Polyvinylpyrrolidinones. Catalytic C(sp3)–H Oxidation

Second-generation chiral-substituted poly-N-vinylpyrrolidinones (CSPVPs) (-)-1R and (+)-1S were synthesized by free-radical polymerization of (3aR,6aR)- and (3aS,6aS)-5-ethenyl-tetrahydro-2,2-dimethyl-4H-1,3-dioxolo[4,5-c]pyrrol-4-one, respectively, using thermal and photochemical reactions. They were produced from respective d-isoascorbic acid and d-ribose. In addition, chiral polymer (-)-2 was also synthesized from the polymerization of (S)-3-(methoxymethoxy)-1-vinylpyrrolidin-2-one. Molecular weights of these chiral polymers were measured using HRMS, and the polymer chain tacticity was studied using 13C NMR spectroscopy. Chiral polymers (-)-1R, (+)-1S, and (-)-2 along with poly-N-vinylpyrrolidinone (PVP, MW 40K) were separately used in the stabilization of Cu/Au or Pd/Au nanoclusters. CD spectra of the bimetallic nanoclusters stabilized by (-)-1R and (+)-1S showed close to mirror-imaged CD absorption bands at wavelengths 200-300 nm, revealing that bimetallic nanoclusters' chiroptical responses are derived from chiral polymer-encapsulated nanomaterials. Chemo-, regio-, and stereo-selectivity was found in the catalytic C-H group oxidation reactions of complex bioactive natural products, such as ambroxide, menthofuran, boldine, estrone, dehydroabietylamine, 9-allogibberic acid, and sclareolide, and substituted adamantane molecules, when catalyst Cu/Au (3:1) or Pd/Au (3:1) stabilized by CSPVPs or PVP and oxidant H2O2 or t-BuOOH were applied. Oxidation of (+)-boldine N-oxide 23 using NMO as an oxidant yielded 4,5-dehydroboldine 27, and oxidation of (-)-9-allogibberic acid yielded C6,15 lactone 47 and C6-ketone 48.

Antioxidative Reactivity of L-Ascorbic Acid and D-Isoascorbic Acid Species towards Reduction of Hexachloroiridate (IV)

The pair [IrCl6]2–/[IrCl6]3– has been demonstrated to be a good redox probe in biological systems while L-ascorbic acid (AA) is one of the most important antioxidants. D-isoascorbic acid (IAA) is an epimer of AA and is widely used as an antioxidant in various foods, beverages, meat, and fisher products. Reductions of [IrCl6]2– by AA and IAA have been analyzed kinetically and mechanistically in this work. The reductions strictly follow overall second-order kinetics and the observed second-order rate constants were collected in the pH region of 0 ≤ pH ≤ 2.33 at 25.0°C. Spectrophotometric titration experiments revealed a well-defined 1 : 2 stoichiometry, namely Δ[AA] : Δ[Ir(IV)] or Δ[IAA] : Δ[Ir(IV)] = 1 : 2, indicating that L-dehydroascorbic acid (DHA) and D-dehydroisoascorbic acid (DHIA) were the oxidation products of AA and IAA, respectively. A reaction mechanism is suggested involving parallel reactions of [IrCl6]2– with three protolysis species of AA/IAA (fully protonated, monoanionic, and dianionic forms) as the rate-determining steps and formation of ascorbic/isoascorbic and ascorbate/isoascorbate radicals; in each of the steps, [IrCl6]2– acquires an electron via an outer-sphere electron transfer mode. Rate constants of the rate-determining steps have been derived or estimated. The fully protonated forms of AA and IAA display virtually identical reactivity whereas ascorbate and isoascorbate monoanions have a significant reactivity difference. The ascorbate and isoascorbate dianions are extremely reactive and their reactions with [IrCl6]2– proceed with the diffusion-controlled rate. The species versus pH and the species reactivity versus pH distribution diagrams were constructed endowing that the ascorbate/isoascorbate monoanionic form dominated the total reactivity at physiological pH. In addition, the value of pKa1 = 3.74 ± 0.05 for IAA at 25.0°C and 1.0 M ionic strength was determined in this work.

Rice bran oil deacidification by immobilized Aspergillus Niger lipase catalyzed esterification with D-isoascorbic acid

The main challenge associated with the upgrading of crude rice bran oil (RBO) rests with their high content of free fatty acids (FFA). In this study, we describe a green and sustainable process for the deacidification of high-acid RBO using d-isoascorbic acid as a novel acyl acceptor in combination with a newly prepared immobilized Aspergillus Niger lipase (ANL). The process contributed a high deacidification efficiency of 97.53 % with a desirable d-isoascorbic acid ester (DIAE) content of 36.10 %. The immobilized ANL could be used consecutively for at least 10 batches with only 7.86 % of activity loss. Scale-up reaction was implemented to verify the amenability of the procedure, and a low acid value of 1.46 mg KOH/g conformed to the quality criteria of edible RBO was then obtained. Physicochemical indices analysis indicated that this procedure was amicable to bioactive phytochemicals in RBO. In addition, the Rancimat test suggested that this process greatly improved the shelf life of deacidified RBO due to the formation of DIAE. This is the first time that d-isoascorbic acid has been used in the refining of RBO. Overall, we report an economically and efficiently viable process for the upgrading of high-acid RBO.

Design of water-based annulus protection fluid for CO2 flooding injection well

To solve the issue that casing and tubing can be easily corroded in the injection well of CO 2 flooding, a novel water-based annulus protection fluid suitable for injection well in CO 2 flooding was developed. Firstly, the appropriate additives, such as the deoxidizer, inhibitor, bactericide, pour point depressant and density regulators, were selected according to the service environment of wellbore. On this basis, the synergism among the additives was evaluated. Then, the ratio of additives was optimized to form the formulation of water-based annulus protection fluid. Finally, the performance evaluation of the water-based annulus protection liquid was evaluated. The results showed the composition of the water-based annulus protection fluid was commercial corrosion inhibitor (XCN20) (1500 ppm), CT4-42 bactericide (1 g/L), D-isoascorbic acid sodium deoxidizer (3 g/L), sodium formate (100 g/L), glycol 20%. The density of the protection fluid was 1.01–1.17 g/cm 3 , and its freezing point was - 2–20 °C. The dissolved oxygen content in the injected water was controlled within 0.3 ppm by using the protection liquid. The corrosion inhibition rate of the water-based annulus protection liquid was higher than 98% in aqueous phase, and the corrosion rate of steel reached the corrosion control index of oil field (0.076mm/a) in gas-aqueous phase. • A method for the preparation of water-based annulus protection fluid was provided. • Density of water-based annulus protection fluid was 1.01–1.17 g/cm 3 , and its freezing point is - 2 - - 20 °C. The dissolved oxygen content in the injected water was controlled within 0.3 ppm. • Corrosion inhibition rate of water-based annulus protection liquid was higher than 98% in SC CO 2 aqueous phase.

Analysis of citric acid and D-isoascorbic acid in beverages by High performance liquid chromatography

In this study, high performance liquid chromatography (HPLC) was used to analysis the content of citric acid and D-isoascorbic acid in beverages. The samples were separated by C18 chromatography column, 0.1 % phosphoric acid solution was used as the mobile phase with the flow rate of 0.5 mL/min, the column temperature was 35 °C, and the detection wavelength was 210 nm. The results showed that the content of citric acid and D-isoascorbic acid has a good linear correlation (r>0.99) within the range of 50 μg to 200 μg. The selectivity, recovery and precision of citric acid and D-isoascorbic acid were suitable. Meanwhile, this method could be used to detect the content of citric acid and D-isoascorbic acid in beverages.

One-pot synthesis method of copper nanoparticles in air

A feasible one-pot synthesis method for the preparation of copper nanoparticles under ambient atmosphere is put forward. Copper oxide and D-isoascorbic acid were chosen as the copper precursor and mild reducing agent, respectively. Oleylamine and octylamine were selected as the capping agents. The effects of the amount and alkyl chain length of capping agent on the synthesis of copper nanoparticles were studied. Antioxidised copper nanoparticles were prepared successfully without the protection of inert atmosphere. The minimum average size of obtained copper nanoparticles was 149 ± 11 nm.

A stimuli-responsive fluorescence platform for simultaneous determination of d-isoascorbic acid and Tartaric acid based on Maillard reaction product

An activatable fluorescence monitoring platform based on a novel Maillard reaction product from d-glucose and L-arginine was prepared through a facile one-pot approach and applied for simultaneous detection of d-isoascorbic acid and tartaric acid. In this work, the new Maillard reaction product GLA was first obtained, and its fluorescence intensity can be effectively quenched by KMnO4, resulting from a new complex (GLA-KMnO4) formation between GLA and KMnO4. Upon addition of d-isoascorbic acid or tartaric acid, an enhanced fluorescence was observed under the optimumed experimental conditions, indicating a stimuli-responsive fluorescence turn on platform for d-isoascorbic acid or tartaric acid can be developed. The corresponding experimental results showed that this turn on fluorescence sensing platform has a high sensitivity for d-isoascorbic acid or tartaric acid, because the detection limits were 5.9μM and 21.5μM, respectively. Additionally, this proposed sensing platform was applied to simultaneously detection of d-isoascorbic acid and tartaric acid in real tap water samples with satisfactory results.

The nonlinear optical properties of the monoclinic d-isoascorbic acid crystal

d-Isoascorbic acid (C6H8O6) crystals belonging to the monoclinic space group P21 are grown from aqueous solution employing slow cooling technique. The grown crystals possess blocky morphology with (100) (010) and (001) prominent faces. Thermal analysis shows that the crystals are stable up to 162 °C and decompose immediately after melting. The optical transmission lower cutoff is determined to be 300 nm. The Kleinman conjecture, applicable to second-order nonlinear coefficients, was violated as the optical transmission was dependent on the state of the incident light polarization. The principal dielectric frame of the crystal was determined using conoscopy and is found to be rotated about the crystallographic b-axis. Non-collinear SHG rings up to second order were observed which helped to locate phase matching directions. The second harmonic conversion efficiency of the crystal is measured to be 3× that of a KDP crystal by both single crystal phase matching and Kurtz powder techniques. Surface laser damage thresholds at 1064 and 532 nm are determined to be 9.7 and 4.2 GW/cm2, respectively.

Quantitation of ascorbic acid in Arabidopsis thaliana reveals distinct differences between organs and growth phases

Optimal plant growth is the result of the interaction of a complex network of plant hormones and environmental signals. Ascorbic acid (AsA) is a crucial antioxidant in plants and is involved in the regulation of cell division, cell expansion, photosynthesis and hormone biosynthesis. Quantitative analysis of AsA in Arabidopsis thaliana organs was conducted using HPLC with d-isoascorbic acid (Iso-AsA) as an internal standard. Analysis revealed fluctuations in the levels of AsA in different organs and growth phases when plants were grown under standard conditions. AsA concentrations increased in leaves in direct proportion to leaf size and age. Young siliques (seed set stage) and flowering buds (open and unopened) showed the highest levels of AsA. A relationship was found between the level of AsA and indole acetic acid (IAA) in leaves, stems, flowers, and siliques and the highest level of IAA and AsA were found in the flowers. In contrast, the lowest level of the plant hormone, salicylic acid, was found in the flowers, and the highest quantity measured in the leaves. Consequently, AsA has been found to be a multifunctional molecule that is involved as a key regulator of plant growth and development.

A novel multicomponent redox polymer nanobead based high performance non-enzymatic glucose sensor

The fabrication of a highly sensitive electrochemical non-enzymatic glucose sensor based on copper nanoparticles (Cu NPs) dispersed in a graphene (G)-ferrocene (Fc) redox polymer multicomponent nanobead (MCNB) is reported. The preparation of MCNB involves three major steps, namely: i) the preparation of a poly(aniline-co-anthranilic acid)-grafted graphene (G-PANI(COOH), ii) the covalent linking of ferrocene to G-PANI(COOH) via a polyethylene imine (PEI), and iii) the electrodeposition of Cu NPs. The prepared MCNB (designated as G-PANI(COOH)-PEI-Fc/Cu-MCNB), contains a conductive G-PANI(COOH), electron mediating Fc, and electrocatalytic Cu NPs that make it suitable for ultrasensitive non-enzymatic electrochemical sensing. The morphology, structure, and electro activities of MCNB were characterized. Electrochemical measurements showed that the G-PANI(COOH)-PEI-Fc/Cu-MCNB/GCE modified electrode exhibited good electrocatalytic behavior towards the detection of glucose in a wide linear range (0.50 to 15mM), with a low detection limit (0.16mM) and high sensitivity (14.3µAmM−1cm−2). Besides, the G-PANI(COOH)-PEI-Fc/Cu-MCNB/GCE sensor electrode did not respond to the presence of electroactive interferrants (such as uric acid, ascorbic acid, and dopamine) and saccharides or carbohydrates (fructose, lactose, d-isoascorbic acid, and dextrin), demonstrating its selectivity towards glucose. The fabricated NEG sensor exhibited high precision for measuring glucose in serum samples, with an average RSD of 4.3% and results comparable to those of commercial glucose test strips. This reliability and stability of glucose sensing indicates that G-PANI(COOH)-PEI-Fc/Cu-MCNB/GCE would be a promising material for the non-enzymatic detection of glucose in physiological fluids.

Synthesis of 2,3-Dideoxy-2-fluoro-2,3-endo-methylene- and 2,3-Dideoxy-2-fluoro-3-C-hydroxymethyl-2,3-endo-methylene-pentofuranoses and Their Use in the Preparation of Conformationally Locked Bicyclic Nucleosides

Construction of protected 2,3-dideoxy-2-fluoro-2,3-endo-methylene-pentofuranoses from d-glyceraldehyde and 2,3-dideoxy-2-fluoro-3-C-hydroxymethyl-2,3-endo-methylene-pentofuranoses from d-isoascorbic acid, via Simmons-Smith-type stereoselective cyclopropanations on the respective fluoroallyl alcohols, is described. Synthesis of the corresponding conformationally locked sugar modified uridine and guanosine nucleosides was achieved via Vorbrüggen or Mitsunobu methodologies. Stereochemical confirmation of the novel nucleosides was performed on the basis of 2D NOESY NMR experiments. Analysis of 2',3'-dideoxy-2'-fluoro-3'-C-hydroxymethyl-2',3'-endo-methylene-uridine by X-ray crystallography yielded the principal conformational parameters and indicated that the furanoid ring adopted an (o)E/(o)T1, East pucker. The uridine and guanosine nucleosides were found to be inactive in the hepatitis C virus (HCV) cell-based replicon assay, which was corroborated on examination of the corresponding nucleoside triphosphates against the HCV NS5B polymerase.

Process optimization and kinetic evaluation for biosynthesis of D-isoascorbyl stearate.

The synthesis of D-isoascorbyl stearate from D-isoascorbic acid and stearic acid with immobilized lipase (Novozym(®)435) as catalyst was studied. Response surface methodology and Box-Behnken design with six variables and three levels were employed to evaluate the effects of processing conditions on the conversion of D-isoascorbic acid. The results confirmed that the response surface method and statistical analysis were proved to be useful in developing optimal conditions for D-isoascorbyl stearate synthesis. The optimum conditions were predicted as follows: reaction temperature 48°C, reaction time 17.7h, immobilized lipase amount 50.0% (w/w, of D-isoascorbic acid), substrate molar ratio 9:1 (stearic acid to D-isoascorbic acid), D-isoascorbic acid concentration 0.14mol/L (based on solvent), 4A molecular sieve addition 200g/L (based on solvent), and the optimal conversion was 90.6%. Through the kinetics model fitting of the esterification, it was considered that the esterification conformed to a Ping-Pong bi-bi kinetic model with D-isoascorbic acid inhibition, and the obtained kinetic constants showed that the inhibition of D-isoascorbic acid and the enzyme affinity to substrate were abate with the increase of the reaction temperature.

Molecular expression and functional activity of vitamin C specific transport system (SVCT2) in human breast cancer cells

The main goal of this study is to investigate the expression of sodium dependent vitamin C transport system (SVCT2). Moreover, this investigation has been carried out to define uptake mechanism and intracellular regulation of ascorbic acid (AA) in human breast cancer cells (MDA-MB231, T47D and ZR-75-1). Uptake of [14C] AA was studied in MDA-MB231, T47D and ZR-75-1 cells. Functional parameters of [14C] AA uptake were delineated in the presence of different concentrations of unlabeled AA, pH, temperature, metabolic inhibitors, substrates and structural analogs. Molecular identification of SVCT2 was carried out with reverse transcription-polymerase chain reaction (RT-PCR). Uptake of [14C] AA was studied and found to be sodium, chloride, temperature, pH and energy dependent in all breast cancer cell lines. [14C] AA uptake was found to be saturable, with Km values of 53.85±6.24, 49.69±2.83 and 45.44±3.16μM and Vmax values of 18.45±0.50, 32.50±0.43 and 33.25±0.53pmol/min/mg protein, across MDA-MB231, T47D and ZR-75-1, respectively. The process is inhibited by structural analogs (l-AA and d-iso AA) but not by structurally unrelated substrates (glucose and PAHA). Ca++/calmodulin and protein kinase pathways appeared to play a crucial role in modulating AA uptake. A 626bp band corresponding to a vitamin C transporter (SVCT2) based on the primer design was detected by RT-PCR analysis in all breast cancer cell lines. This research article describes AA uptake mechanism, kinetics, and regulation by sodium dependent vitamin C transporter (SVCT2) in MDA-MB231, T47D and ZR-75-1 cells. Also, MDA-MB231, T47D and ZR-75-1 cell lines can be utilized as a valuable in vitro model to investigate absorption and permeability of AA-conjugated chemotherapeutics.

Functional Characterization and Molecular Identification of Vitamin C Transporter (SVCT2) in Human Corneal Epithelial (HCEC) and Retinal Pigment Epithelial (D407) Cells

Purpose: The main goal of this study is to investigate the existence of sodium-dependent vitamin C transport system (SVCT2) and to define time-dependent uptake mechanism and intracellular regulation of ascorbic acid (AA) in human corneal epithelial (HCEC) and human retinal pigment epithelial (D407) cells.Methods: Uptake of [14C] AA was studied in HCEC and D407 cells. Functional aspects of [14C] AA uptake were studied in the presence of different concentrations of unlabeled AA, pH, temperature, metabolic inhibitors, substrates and structural analogs. Molecular identification of SVCT2 was examined with reverse transcription–polymerase chain reaction (RT-PCR).Results: Uptake of [14C] AA was observed to be sodium, chloride, temperature, pH and energy-dependent in both cell lines. [14C] AA uptake was found to be saturable, with Km values of 46.14 ± 6.03 and 47.26 ± 3.24 μM and Vmax values of 17.34 ± 0.58 and 31.86 ± 0.56 pmol/min/mg protein, across HCEC and D407 cells, respectively. The process is inhibited by structural analogs (L-AA and D-Iso AA) but not by structurally unrelated substrates (glucose and PAHA). Ca++/calmodulin and protein kinase pathways play an important role in modulating uptake of AA. A 626 bp band corresponding to a vitamin C transporter (SVCT2) has been identified by RT-PCR analysis in both the cell lines.Conclusion: This research article reports regarding the ascorbic acid uptake mechanism, kinetics and regulation by sodium dependent vitamin C transporter (SVCT2) in HCEC and D407 cells. Also, SVCT2 can be utilized for targeted delivery in enhancing ocular permeation and bioavailability of highly potent ophthalmic drugs.

Measurement and Correlation for the Solid Solubility of Antioxidants d-Isoascorbic Acid and Calcium l-Ascorbate Dihydrate in Supercritical Carbon Dioxide

The central task of this research is devoted to the measurement of the solubility of two antioxidants—d-isoascorbic acid and calcium l-ascorbate dihydrate—in supercritical carbon dioxide. The experiment, using a semiflow type apparatus, takes data at various temperatures, over pressures ranging from 12 MPa to 24 MPa. The acquired data are then processed numerically—with the aid of semiempirical equations proposed by Chrastil and by Mendez-Santiago and Teja—to find the correlated relationship. The correlated results from both equations yield satisfactory results with an average absolute relative deviation (AARD) under 5 % when optimally fitted parameters are chosen.